Macro- and micromechanical behavior of oil palm wood (Elaeis guineensis Jacq.): tensile, compression and bending properties

Abstract

This study investigates the macromechanical and micromechanical behavior of oil palm wood by testing the elastomechanical properties in bending, compression parallel and perpendicular and tension parallel and perpendicular to the vascular bundles of small-size test specimen depending on the position within the trunk, the density and the number of vascular bundles per unit area as well as the plantation site. All properties tested show a much higher exponential increase with the density, following power law relationships with exponents > 1, than common wood species and a significant gradient over both trunk height and cross section. Oil palm wood can be seen as a unidirectional long-fiber-reinforced bio-composite, if vascular bundles are considered as reinforcements (fibers) and parenchymatous ground tissue as matrix. The adapted rule-of-mixture based on the number of vascular bundles per unit area can be confirmed for the density, but not for the tensile properties, because the number of vascular bundles per unit area and share of fibers within the bundles is greater in the periphery than in the trunk central tissue. Furthermore, cell wall thickening over time is more pronounced in the peripheral than in the central tissue and more at the bottom than near the top. Different from small test specimens from common wood species, the compression strength exceeds the tensile strength: f_c,0 : f_m : f_t,0 is 1.4 : 2.2–1.2 : 1. The performance indices for minimum weight design by Ashby and coworkers are comparable to that for coconut and date palm wood.